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Cause and effect in time dependent flow of thermoplastic melts—a review
Author(s) -
Schreiber H. P.
Publication year - 1966
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760060407
Subject(s) - viscometer , materials science , extrusion , melt flow index , viscosity , capillary action , thermoplastic , viscosity index , composite material , relative viscosity , flow properties , rheology , thermodynamics , mechanics , polymer , scanning electron microscope , base oil , physics , copolymer
The factors leading to time dependnt variations of melt viscosity during capillary extrusion of thermoplastics are reviewed. An initial increase in melt viscosity has been attributed to melt elasticity while three mechanisms are cited to account for a subsequent drop in melt viscosity, which may or may not attain a steady‐state value. These are frictional heational heating of the melt, increasing shear stress as the viscometer reservoir empties, and cain orientation. The relative importance of the mechanisms is examined for various melts and the importance of time effects is discussed in terms of their influence on standard flow evaluations, such as the melt index determination.